class_docstr: MRC Sample class to hold the mrc data info and provide atomic operations.
docstr: Insert item before index of field value.
  
  :param str field: field name
  :param int index: modified scope
  :param items: inserted item
  :return: modified Sample
docstr_tok: ["Insert","item","before","index","of","field","value",".",":","param","str","field",":","field","name",":","param","int","index",":","modified","scope",":","param","items",":","inserted","item",":","return",":","modified","Sample"]
code: def insert_field_before_index(self, field, index, items):
      r"""
      Insert item before index of field value.
  
      :param str field: field name
      :param int index: modified scope
      :param items: inserted item
      :return: modified Sample
  
      """
      return self.insert_field_before_indices(field, [index], [items])
  
imports: from .cnsample import CnSample
  from ..field import Field, CnTextField
  from ....common.utils.list_op import normalize_scope
  from ....common.preprocess.nltk_res_load import ModelManager
  from ....common.settings import *
  from nltk.stem.lancaster import LancasterStemmer
  from copy import deepcopy
label_desc: Use image node_id 15 for calling the MRCCnSample obj's underlying member method code with example usage: obj.insert_field_before_index(field, index, items) and returns: self